Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
thuc van » thuc vat, thuc dan, thuc va
van hanh » van thanh, ban hanh, van anh
lai cua » hai cua, lai chau, thai cua
tu dan » tuc dan, tu ban, cu dan
dan ky » van ky
co hoi » co hoc, co loi
van am » van nam, van lam, van dam
o hoi » o hoc, o hai, o hoa

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: tu dan ky nang ((o hoi) OR (co hoi)). hieu van am thuc van hanh ((dai cua) OR (lai cua)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu dan ky nang ((o hoi) OR (co hoi)). hieu van am thuc van hanh ((dai cua) or (lai cua)) tre~".
• Adding a wildcard symbol may retrieve word variants: tu dan ky nang ((o hoi) OR (co hoi)). hieu van am thuc van hanh ((dai cua) or (lai cua)) tre*.